GB2156085A

GB2156085A - Testing dynamoelectric machines

Info

Publication number: GB2156085A
Application number: GB08501581A
Authority: GB
Inventors: Einar Andersson
Original assignee: AELMHULTS ELEKTROMEK ANDERSSON
Current assignee: AELMHULTS ELEKTROMEK ANDERSSON
Priority date: 1984-02-06
Filing date: 1985-01-22
Publication date: 1985-10-02
Also published as: SE8400591D0; DE3502179A1; SE8400591L; GB8501581D0

Abstract

An apparatus for connecting a pulsating voltage across a winding upon such inspection of an electric machine, in particular a three-phase machine, as aims at detecting a stator and/or rotor winding fault, is provided with a current source (2) and an oscillator (1) connected to aid current source via a switch (3). An ammeter (6) is connected in one output (4) of the oscillator (1) which is adapted to supply a pulsating voltage of variable pulse width, said pulsating voltage being intended for connection across the said winding, and said pulse width being variable to provide a suitable deflection of the ammeter (6) when the pulsating voltage is connected across the winding. <IMAGE>

Description

SPECIFICATION Apparatus for connecting a pulsating voltage across a winding upon inspection of an electric machine The present invention relates to an apparatus for connecting a pulsating voltage across a winding upon such inspection of an electric machine, especially a three-phase machine, as aims at detecting a stator and/or rotor winding fault, said apparatus comprising a current source and an oscillator which is connected to said current source via a switch and is adapted to provide a pulsating voltage for connection across said winding.

In conventional fault detection technique, the electric machine to be inspected usually is dismantled. Especially upon inspection of the rotor of an electric machine, fault detection is carried out entirely mechanically or visually.

Thus, considerable disadvantages and difficulties are encountered which greatly increase the cost of repairing the machine. Many times, the difficulties encountered in the inspection of electric machines in accordance with conventional fault detection technique are so great that it is preferred to replace the machine instead of carrying out fault detection and subsequent repairs.

These disadvantages and difficulties are eliminated by a fault detection method previously known from French patent specification 69/00920, in which method use is made of an apparatus which is of the above-mentioned type and, furthermore, has a transformer, the primary winding of which is connected to the oscillator outputs. The secondary winding of the transformer has a plurality of terminals for different voltages, and one of its ends is connected to an input of a stopping switch.

The outputs of the secondary windings are connected each to one input of the stepping switch, the output of which is a rotary arm leading to a first connection of a winding in the machine to be inspected. The other end of the secondary winding is connected, via a pointer instrument and a fuse, to a second connection for the winding. When the switch is closed, there is obtained between said connections a pulsating voltage, the level of which is selected such by means of said stepping switch that a suitable deflection is obtained on the pointer instrument when a winding of the machine to be inspected is connected between said connections.

This prior art fault detection technique and the method of utilising the prior art apparatus are described in detail in the above-mentioned French patent specification.

The prior art apparatus weighs about 5 kilograms and thus is portable. Nevertheless, this is felt to be no little load when the apparatus must be carried up to high-level positions or positions difficult of access, for example when the electric motor to be inspected is mounted in an overhead fan casing or the like. Moreover, this known apparatus suffers from the disadvantage that its current consumption upon fault detection is veryhigh.

It therefore is the object of this invention to provide an apparatus which has less weight and lower current consumption and in which the transformer which is the heaviest part of the prior art apparatus, is dispensed with, while at the same time however retaining the possibility of controlling the deflection of a pointer instrument when a winding in the machine to be inspected is connected between the terminals of the apparatus.

According to the present invention, this object is achieved by means of an apparatus which is of the type mentioned by way of introduction and which is characterised in that the oscillator is adapted to produce a pulsating voltage of variable pulse width.

By varying the pulse width according to a winding mounted in the machine to be inspected and connected between the oscillator outputs, it is possible to adjust the deflection of an ammeter which preferably is connected to one output of the oscillator, to a suitable reading value.

An embodiment of the present invention will be described in more detail below, reference being had to the accompanying drawings. In the drawings Figure 1 is a schematic circuit diagram of the apparatus according to the invention; Figure 2 illustrates several different voltage pulse trains provided by the apparatus; Figure 3 is a detailed circuit diagram of the apparatus.

The apparatus shown in Figs. 1 and 3 comprises an oscillator 1 which, via a switch 3, is connected to a d.c. source 2 in the form of a 9-volt battery. Via its outputs 4 and 5, the oscillator provides a pulsating a.c. voltage in the form of a square pulse train of variable pulse width. Connected to one output 4 of the oscillator 1 is a pointer instrument 6 which, in this case, is an ammeter. Furthermore, a fuse 7 is connected to the output 4. The outputs 4 and 5 terminate each in one terminal 8 and 9, respectively, for connection to a winding of the machine to be inspected. The oscillator 1 has a setting knob 10 for continuous control of the pulse width of the a.c. voltage provided. Fig. 2 shows three examples of the voltage across the terminals 8 and 9 in the form of a pulse train having the same amplitude or level, but different pulse widths.By turning the setting knob 10, it is possible to adjust the pulse width (in contrast to the pulse level) in order to obtain on the ammeter 6 a suitable pointer deflection responsive to the winding connected between the terminals 8 and 9.

The construction of the oscillator 1 and the connection of the ammeter 6 and the fuse 7 in the output 4 of the oscillator 1 are shown in detail in Fig. 3, but do not per se constitute a proper part of the invention and therefore are not described in detail. It is, however, part of the invention that oscillator 1 has a member 10 (illustrated in Fig. 1 by means of a setting knob and in Fig. 3 by means of a potentiometer) which is adapted to vary the pulse width in the manner described above.

Because the transformer unit utilised in the prior art apparatus referred to above, can be dispensed with in the apparatus according to the present invention, the weight of the apparatus could be reduced from about 5 kilograms to about 1 kilogram. Furthermore, the current consumption during fault detection could be reduced considerably.

Claims

1. An apparatus for connecting a pulsating voltage across a winding upon such inspection of an electric machine, especially a three-phase machine, as aims at detecting a stator and/or rotor winding fault, said apparatus comprising a current source and an oscillator which is connected to said current source via a switch and is adapted to provide a pulsating voltage for connection across said winding, characterised in that the oscillator is adapted to produce a pulsating voltage of variable pulse width.

2. An apparatus as claimed in claim 1, characterised in that an ammeter is connected to one output of the oscillator.

3. An apparatus for connecting a pulsating voltage across a winding upon inspection of an electric machine, substantially as herein described and illustrated in the accompanying drawings.